Drug applicators such as syringes and drenchers have long been known in the industry. Some of the prior art multi-dose applicators are described in U.S. Pat. Nos. 5,232,459, 5,188,610, 4,738,664, 4,245,757, and 4,020,838 and in the N.J. Phillips 1986 Export Catalogue which are incorporated herein by reference.
Generally, the prior applicators employed a threaded nut screw for attaching the applicator to a drug supply. The use of threaded nut screws for attaching the drug supply to an applicator is time consuming and cumbersome, especially when entire herds of cattle or sheep are being treated.
The prior applicators such as those described in U.S. Pat. Nos. 4,738,664, 4,245,757 and 4,020,838 all possess plunger assemblies that comprise a shaft of a uniform diameter. The uniform diameter shafts fail to compensate for any misalignment of the plunger with the dosage tube or tolerance accumulation.